Prince Charles reveals the one thing he'll stop doing when he becomes king

Prince Charles will stop campaigning about issues he feels passionately about when he becomes king because he has to operate within 'constitutional parameters'.

In a BBC documentary to mark his 70th birthday, the royal says he'll stop advocating topics close to his heart, such as the environment and climate change, when he becomes monarch because his roles of Prince of Wales and king are completely separate.

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Earlier this week during a royal visit to Ghana, Charles was speaking out against plastic pollution and how the next generation deserves better than the 'insanity' of a 'destroyed and damaged' world.

In the upcoming celebratory documentary, Charles was asked about his campaigning, which some people have branded as 'meddling'.

Documentary film-maker John Bridcut revealed the prince 'bridled a bit' at the use of the word 'meddling', and instead argued that he was trying to motivate others to protect the planet.

'If it's meddling to worry about the inner cities as I did 40 years ago, then if that's meddling I'm proud of it,' Charles said.

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'It's vital to remember there's only room for one sovereign at a time, not two. So, you can't be the same as the sovereign if you're the Prince of Wales or the heir.

'But the idea, somehow, that I'm going to go on in exactly the same way, if I have to succeed, is complete nonsense because the two – the two situations – are completely different.'

When asked if his campaigning would carry on when he is king, Charles replied: 'No, it won't. I'm not that stupid.'

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Bridcut concluded: 'People who think he's hanging around, longing to be king, are very mistaken.

'It's not something he's dying to assume because inevitably it will only arise after the death of his mother.'

Prince William and Prince Harry also feature in the documentary, and will speak about how their father used to take them litter picking when they were younger.

William recalled: We thought this is perfectly normal, everyone must do it. We were there with our spikes stabbing the rubbish into black plastic bags.'

Prince, Son And Heir: Charles At 70, will air on BBC One on Thursday, 8 November, at 21:00.